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Heredity and Evolution


Grade 10 -CBSE - Heredity and Evolution – PowerPoint PPT presentation

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Title: Heredity and Evolution

Heredity and Evolution
  • Prepared by
  • Gowri Baskar

  • Also called inheritance or biological
  • It is the passing on of traits from parents to
    their offspring either through asexual
    reproduction or sexual reproduction
  • The offspring cells or organisms acquire the
    genetic information of their parents.
  • Through heredity, variations between individuals
    can accumulate and cause species to evolve by
    natural selection.
  • The study of heredity in biology is genetics.

  • Gene is the unit of inheritance/heredity.
  • Gene is the part of a chromosome which controls
    the appearance of a set of hereditary

  • Evolution is the sequence of gradual changes
    which take place in the primitive organisms over
    millions of years and new species are produced.
    Since, the evolution is of the living organisms,
    so it is called Organic Evolution.
  • Darwins theory of Evolution Charles Robert
    Darwin gave the theory of evolution in his famous
    book, The Origin of Species. The theory of
    evolution proposed by Darwin is known as The
    Theory of Natural Selection. It is also called

Darwins theory of evolution
  • There is natural variation within any population
    and some individuals have more favourable
    variations than others.
  • Population remains fairly constant even though
    all species produce a large number of off
  • This is due to competition or struggle for
    existence between same and different species.
  • The struggle for survival within population
    eliminates the unfit individuals and those with
    favourable variations survive and pass on these
    variations to their progeny to continue. This is
    called natural selection.
  • The favourable variations are accumulated over a
    long time period leading to the origin of a new

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Genotype and Phenotype
  • In humans, eye color is an example of an
    inherited characteristic an individual might
    inherit the "brown-eye trait" from one of the
  • Inherited traits are controlled by genes and the
    complete set of genes within an organism's genome
    is called its genotype.
  • The complete set of observable traits of the
    structure and behavior of an organism is called
    its phenotype.
  • These traits arise from the interaction of its
    genotype with the environment. As a result, many
    aspects of an organism's phenotype are not

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  • Sexual reproduction
  • The mode of reproduction that involves two
    individuals one male and one female.
  • They produce sex cells or gametes which fuse to
    form a new organism.

Father of Genetics
Moravian monk Gregor Mendel
  • The idea of particulate inheritance of genes can
    be attributed to the Moravian monk Gregor Mendel
    who published his work on pea plants in 1865.
  • However, his work was not widely known and was
    rediscovered in 1901.
  • It was initially assumed that Mendelian
    inheritance only accounted for large
    (qualitative) differences, such as those seen by
    Mendel in his pea plants and the idea of
    additive effect of (quantitative) genes was not
    realised until R.A. Fisher's (1918) paper, "The
    Correlation Between Relatives on the Supposition
    of Mendelian Inheritance" Mendel's overall
    contribution gave scientists a useful overview
    that traits were inheritable.
  • His pea plant demonstration became the foundation
    of the study of Mendelian Traits. These traits
    can be traced on a single locus.

Dominant traits
  • The traits that express themselves in an organism
    in every possible combination and can be seen are
    called Dominant traits.
  • In Mendels experiment, we see that tall trait in
    pea plants tends to express more than the short
  • Therefore, the tall trait of the plant is said to
    be dominant over the short trait.

Recessive traits
  • A trait which is not expressed in presence of a
    dominant allele is known as recessive.
  • So, recessive character/trait is present in an
    organism but cannot be seen if a dominant allele

Monohybrid cross
  • When only one character is considered while
    crossing two organisms, then such a cross is
    known as monohybrid cross.
  • The ratio of characters, arising out of this
    cross, at F2 generation is called monohybrid
  • E.g., If tall plant (TT) is crossed with a dwarf
    plant (tt), we get 3 tall1 short plant at the
    end of the F2 generation.
  • So, 31 is monohybrid ratio.
  • Here, the height of the plant is considered at a

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Dihybrid cross
  • When two characters are considered while crossing
    two organisms, then such a cross is known as a
    dihybrid cross.
  • The ratio of characters, arising out of this
    cross, at F2 generation is called dihybrid ratio.
  • E.g., If a plant with round and green pea is
    crossed with a plant with wrinkled and yellow
  • The first generation plants would all have round
    and green pea.
  • On crossing the same for an F2 generation, we
    would observe four combinations of characters in
    the ratio of 9331.
  • Thus, 9331 is the dihybrid ratio.

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Sex determination in humans
  • Mechanism of Sex Determination in Human
    BeingsIn human beings, the sex of the
    individual is genetically determined.
  • Sex determination is the process by which sex of
    a new born individual can be determined.
  •  Human beings have 1 unpaired sex chromosome. Sex
    chromosome of male is XY and of female is XX.
  •  Sex of a child depends on what happens at
  • Father is responsible for the determination of
    the sex of a child.

Sex determination in humans